Low-foaming tensides having good surfactant and cleansing properties are required in household dishwashers, and also have a corresponding use in commercial fields. Thus, solid, pulverized detergents for dishwashers, for example, frequently contain 1-3% by weight of such tensides in addition to the customary ingredients such as pentasodium triphosphate, sodium silicate, sodium carbonate, sodium aluminate, compounds splitting off chlorine and scenting agents. Liquid compositions used for mechanical cleansing and as additives for clear and sparkling clean rinsing can even contain 15-25% by weight of such tensides.
Tensides satisfying the above prerequisites include, for example, propylene oxide-ethylene oxide polymers known under the trade name of "PLURONICS" (U.S. Pat. No. 2,674,619). In these compounds, the molecular units based on propylene oxide have a lipophilic character whereas the segments formed by ethylene oxide are considered hydrophilic.
The tensides structured in this way, however, have the grave disadvantage that they are biodegradable only with great difficulty. In this age where environmental protection has gained increasing significance in all areas, this property, of course, extensively restricts their useability. For example, a biodegradability of at least 80% is required in the Federal Republic of Germany under the "Antipollution Act Regarding Detergents and Cleansing Agents" of Aug. 20, 1975 ("Detergent Law") and the concomitantly issued "Regulation Regarding the Degradability of Anionic and Nonionic Surfactants in Detergents and Cleansing Agents" of Jan. 30, 1977. The criterion is the so-called "OECD Confirmatory Test" by means of which the residual content of a sample solution of nonionic surfactants is determined using the bismuth activity measurement according to Wickbold. Although ethylene oxide-propylene oxide block and copolymers do not meet this requirement, their use was still permitted for another three years during which a replacement was to be found.
In addition to these polymers, containing only ethylene oxide and propylene oxide or perhaps diamines, another class of compounds is utilized for low-foaming tensides in the above-mentioned areas. These can be considered as unilaterally blocked oligomers of ethylene oxide-propylene oxide units (DOS [German Unexamined Laid-Open Application] No. 1,593,043). These compounds are obtained by addition of alkylene oxides to suitable starting compounds having active hydrogen atoms, such as fatty alcohols or alkyl phenols. The character of the resultant tenside can be varied within limits by suitable choice of block or mixed addition. The advantage of these surface-active compounds resides in the fact that they are more susceptible to biological attack than the "PLURONIC" types. Although they fulfill the requirements of the OECD Confirmatory Test, they are still in need of improvement, as was found by testing their degree of complete remineralization.
If it is desired to avoid the danger factor caused by the formation of metabolites which, in turn, resist further degradation or are even toxic, the use of maximally extensively remineralizable compounds must be preferred. Remineralization means that, for example, a compound made up of carbon, hydrogen, and oxygen, as represented by most of the nonionic tensides, for example, is converted into carbon dioxide and water. The requirement for a satisfactory remineralization is met if values of 50% and above are reached in the biodegradation test measuring the degree of complete remineralization. However, this condition is attained only by an extremely gradual reaction of propylene oxide adducts and even more so by butylene oxide adducts, as was demonstrated by investigations of Fischer (VI. Int. Kongr. grenzfl. akt. Stoffe [Sixth International Congress for Surfactants] Zurich, 1972, 3:745 et seq., especially page 747).
The derivatives of such epoxides heretofore used as low-foaming tensides thus do not provide a satisfactory solution to the problem from an ecological viewpoint.